Blocking download of content

ABSTRACT

At least initially blocking client download of certain content and injecting a user verification step for such downloads is disclosed. In some embodiments, client download of a response from a server to a client request is blocked, and instead a notification page with options to accept or decline the server response is provided to the client.

BACKGROUND OF THE INVENTION

Existing computer security solutions typically fail to detect threatssuch as newer viruses whose signatures have not yet been identified.Improved techniques to thwart such threats would be useful.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIGS. 1A-1C are block diagrams illustrating an embodiment of a networkenvironment in which downloads of unknown or untrusted content are notpermitted without user consent.

FIG. 2 is a flow chart illustrating an embodiment of a process forprocessing a response to a client request that is received from aserver.

FIG. 3 is a flow chart illustrating an embodiment of a process fordownloading content that is initially blocked by a firewall.

FIG. 4 is a flow chart illustrating an embodiment of a process forprocessing a client request.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers one or more devices, circuits, and/or processing cores configuredto process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims,and the invention encompasses numerous alternatives, modifications, andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example, andthe invention may be practiced according to the claims without some orall of these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

Drive-by download of malware has become a ubiquitous security threat incomputing. A user visiting a link or opening a file may be forced toalso unknowingly download malicious code and/or content. For example, aweb page downloaded by a user using a web browser may unknown to theuser include malicious code that spawns a background process thatautomatically downloads and executes malware on the user device withoutbeing visible to the user. In many cases, users may not even be aware ofwhen and where their devices got infected. Security software, such asantivirus software, may be employed to protect devices against knownthreats whose signatures are known but may not be very effective atpreventing zero-day exploits whose signatures are not yet known.Improved techniques to thwart drive-by and other downloads of malwareare disclosed herein.

FIGS. 1A-1C are block diagrams illustrating an embodiment of a networkenvironment 100 in which downloads of unknown or untrusted content arenot permitted by firewall 102 without user consent. As depicted in thegiven example, messaging between client 104 and server 106 isfacilitated by firewall 102, which intercepts and enforces a policy forcommunications between client 104 and server 106. In variousembodiments, firewall 102 may comprise a dedicated device or applianceand/or software configured to provide firewall functionality. Forexample, firewall 102 may comprise any appropriate hardware and/orsoftware configuration and/or components for proxying and/or processingcommunications between client 104 and server 106. In some embodiments,firewall 102 is part of a router or gateway device that facilitatescommunications between a private, internal network of which client 104is a member and a public or other external network such as the Internetvia which server 106 is accessible. Although depicted as a separateblock in FIGS. 1A-1C, in other embodiments, firewall 102 may comprise ahost-based firewall that is part of client 104. The various entitiescomprising network environment 100 may communicate over any combinationof public and/or private networks such as a LAN, WAN, the Internet,etc., using any appropriate communication protocols such as HTTP(Hypertext Transfer Protocol), SSL (Secure Sockets Layer), FTP (FileTransfer Protocol), etc.

Messaging between client 104 and server 106 is monitored by firewall102. In the given example, a content request to server 106 from client104 is intercepted by firewall 102 and forwarded by firewall 102 toserver 106. In various embodiments, the content request may result froman action of a user of client 104 and/or an application or processrunning on client 104. A response from server 106 to the client requestis initially received by firewall 102. In some embodiments, the responsefrom server 106 is analyzed by firewall 102 to determine, for instance,whether the response is from a trusted or untrusted source and/orwhether the response comprises safe or potentially suspect content suchas an executable file download. If the response is determined byfirewall 102 to be trusted, the response from server 106 is directlyforwarded to client 104 as depicted in FIG. 1A.

However, if the response is determined by firewall 102 to be receivedfrom an unknown or untrusted source that, for example, is not includedin a whitelist of trusted sources or is included in a blacklist of knownmalicious sources, and/or if the received response includes potentiallysuspect content, in some embodiments, firewall 102 drops the responseand terminates the existing session between client 104 and server 106.In some such cases, firewall 102 instead forwards to client 104 anotification page as depicted in FIG. 1B that prompts the user of client104 to accept or decline the server response. In some embodiments, thenotification page comprises an HTML (HyperText Markup Language) pagethat is displayed at client 104 by a browser. In some embodiments, thenotification page has an associated timer and expires if no response isreceived within a prescribed timeframe. By at least initially blockingpotentially suspect content and acquiring user consent beforedownloading such content, firewall 102 provides a failsafe to preventclient 104 from inadvertently downloading malicious content. If the userof client 104 does not consent to the download and/or selects an optionto decline the download via the notification page, the content is notdownloaded to client 104, thus thwarting a potentially malicious backendprocess spawned on the client from downloading content that could beused to further infect or compromise the client.

If the suspect content is in fact legitimate, the user of client 104 mayselect an option in the notification page to accept the server response.In some cases, user selection of an option in the notification page toaccept the server response results in a web browser of client 104 tosend a second or subsequent request for the content to server 106 asdepicted in FIG. 1C. In some cases, the second or subsequent requestcomprises a new session between client 104 and server 106 since in someembodiments a previous session between client 104 and server 106 isterminated or reset when the response from server 106 to the previousrequest from client 104 is dropped by firewall 102, e.g., in FIG. 1B. Asfurther described below, in some embodiments, the second or subsequentrequest from client 104 includes an indication that the server responseto the request has been approved for download by the user of client 104.In some embodiments, the indication comprises a cookie or otherparameter that is set or configured and included with the second orsubsequent request when the user of client 104 selects an option in thenotification page to accept the server response. As depicted in FIG. 1C,firewall 102 receives the second or subsequent request from client 104and forwards the second or subsequent request to server 106. A responsefrom server 106 to the second or subsequent request from client 104 isrecognized by firewall 102 as being approved by the user of client 104and is thus forwarded to client 104.

In some embodiments, a response received from an unknown or untrustedsource and/or determined to comprise suspect content is not immediatelydiscarded by firewall 102 as described with respect to FIG. 1B but isinstead temporarily locally stored or cached, e.g., in the proxyenvironment, by firewall 102 while a notification page is sent to client104 for a user to verify the download. In such cases, if the user ofclient 104 selects an option to accept the download, the locally storedresponse from server 106 is forwarded by firewall 102 to client 104. Inthis embodiment, there may not be a need for a second or subsequentrequest from client 104 and a corresponding response from server 106 asdescribed with respect to FIG. 1C. However, if the user of client 104does not select an option to accept the download within a timeout windowof the notification page and/or selects an option to decline thedownload, the locally stored response from server 106 is purged byfirewall 102 and not forwarded to client 104.

FIG. 2 is a flow chart illustrating an embodiment of a process forprocessing a response to a client request that is received from aserver. In some embodiments, process 200 is employed by firewall 102 ofFIGS. 1A-1C, for example, while monitoring HTTP and/or other traffic.Process 200 starts at 202 at which a response to a content request froma client is received from a server. At 204, it is determined whether theclient has already approved the response, i.e., approved download of thecontent comprising the response, for example, via process 300 of FIG. 3.If it is determined at 204 that the response has not already beenapproved by the client, the response is parsed at 206. For example, step206 may include parsing or decoding the response to extract informationsuch as an associated URL (Uniform Resource Locator) or URI (UniformResource Identifier), header information such as information associatedwith the host or server from which the response is received, the type ofcontent included in the response, etc. In some embodiments, step 206includes determining whether the response comprises a file download,such as an executable file download.

At 208, it is determined whether the response is trusted based on apolicy enforced by firewall 102. In some embodiments, step 208 includesdetermining whether the response is trusted based on the source of theresponse and/or the type of content included in the response. Forexample, a response may be deemed to be trusted if the source of theresponse is included in a whitelist of trusted applications or sources(e.g., Microsoft Updates, Java Updates, Adobe Updates, etc.) and may bedeemed to be untrusted otherwise. Likewise, a response may be deemed tobe untrusted if the source of the response is included in a blacklist ofknown malicious sites or otherwise untrusted sources. Such white and/orblack lists for policing traffic crossing firewall 102 may be configuredby the provider of firewall 102, may be individually configured byentities using firewall 102, and/or may be changed or updated over timeas applicable. In some cases, the type of content included in theresponse may be employed to determine whether the response is trusted.For instance, a response that comprises an executable file may not betrusted from any source or if the source is not included in a whitelistof trusted sources. In some embodiments, determining whether theresponse is trusted is based at least in part on parsing the associatedclient request and determining, for example, whether the requestedcontent is trusted and/or whether the host or server to which therequest is directed is trusted, i.e., included in a whitelist.

If it is determined at 204 that the response has already been approvedby the client or if it is determined at 208 that the response istrusted, the response is forwarded to the client at 210. If it isdetermined at 208 that the response is not trusted, the response isblocked from the client and instead a notification page informing theuser of the client of the response and prompting the user to accept ordecline the response is forwarded to the client at 212. In someembodiments, the notification page comprises an HTML page that isdisplayed at the client by a browser and provides user options to acceptor decline the response. Code associated with the notification page mayat least in part be encoded, obfuscated, and/or encrypted. In someembodiments, the notification page includes a unique identifier that isgenerated, for example, by firewall 102. In some such cases, the uniqueidentifier comprises the value of a cookie. When a user selects anoption of the notification page to accept the response, in someembodiments, a browser cookie is set to the unique identifier andprovided with a second or subsequent request by the client for thecontent. In some embodiments, firewall 102 is configured to concludethat the response to the second or subsequent request is approved by auser of the client, for example, if the cookie value received in thesecond or subsequent request has not timed-out and matches theidentifier provided with the notification page at 212. In someembodiments, step 212 includes terminating or dropping a current flow orsession between the client and the server, which in some cases comprisessending a reset to the client and/or server. In some embodiments, step212 includes dropping or discarding the response received at step 202.In other embodiments, the response received at step 202 may betemporarily stored and/or cached by firewall 102 so that the responsecan be forwarded to the client if the user of the client selects anoption to accept the response.

FIG. 3 is a flow chart illustrating an embodiment of a process fordownloading content that is initially blocked by firewall 102. In someembodiments, process 300 is employed by client 104 of FIGS. 1A-1C.Process 300 starts at 302 at which a notification page is received bythe client from firewall 102 that informs the user of the client of aserver response to a content request from the client and prompts theuser to accept or decline the response. At 304, an indication of aselection of an option of the notification page to accept download ofthe server response is received from a user of the client. In someembodiments, user selection of the option to accept the server responseat 304 invokes a piece of JavaScript or other code of the notificationpage that sets a browser cookie value to a unique identifier associatedwith the notification page. At 306, a second or subsequent request forthe content that includes the set cookie is sent by the client to theserver. If the cookie is valid (e.g., if the cookie value has not timedout and/or if the cookie value matches the identifier of thenotification page of step 302), a response to the second or subsequentrequest for the content is received by the client at 308 from the servervia firewall 102. However, if the cookie is not valid (e.g., because thecookie value has timed out and/or if the cookie value does not match theidentifier of the notification page of step 302), process 300 continuesat 302 at which a new notification page with a new identifier isreceived from firewall 102. Although not shown in the flow chart of FIG.3, if the user of the client does not respond to the notification pageof 302 and/or selects an option of the notification page to decline theserver response, the server response is effectively blocked by firewall102 from being sent or downloaded to the client.

FIG. 4 is a flow chart illustrating an embodiment of a process forprocessing a client request. In some embodiments, process 400 isemployed by firewall 102 of FIGS. 1A-1C. Process 400 starts at 402 atwhich a content request from a client directed to a server is receivedor intercepted by firewall 102. At 404, the request is parsed todetermine whether it includes a cookie (or other parameter oridentifier) that indicates that a server response to the request hasbeen approved by a user of the client. If it is determined at 404 thatthe request does not include such a cookie, the request is forwarded tothe server at 406. If it is determined at 404 that the request includessuch a cookie, it is determined at 408 whether the cookie is valid,e.g., by determining whether or not the cookie has timed-out and/orwhether the cookie value matches an identifier included with anotification page previously sent to the client in response to a requestfor the same content as the request of 402. If it is determined at 408that the cookie is not valid, a notification page that includes a new ordifferent identifier is forwarded to the client at 410. If it isdetermined at 408 that the cookie value is valid, it is concluded at 412that the server response to the request received at 402 has already beenapproved by the user of the client and that it is not to be blocked fromthe client, and the request from the client is subsequently forwarded tothe server at 406.

Although some of the given examples describe using a cookie, any otherappropriate technique to obtain and/or identify user approval of aserver response may be employed in other embodiments. For example, insome embodiments, messages to and from firewall 102 may be handled at aclient by a dedicated agent running on the client that also handlesobtaining user verification for downloads of content. As described, byat least initially blocking untrusted content and injecting a userverification step for client downloads of such content, firewall 102provides a mechanism to better protect a client from inadvertentlydownloading malware or other malicious content.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A method, comprising: receiving at a processor ofa firewall appliance a response from a server to a first request forcontent originating from a client of a private network, wherein thefirewall appliance is configured to intercept communications between theclient and the server; determining at the processor that the response isnot known to be safe; caching the response to the first request at thefirewall appliance; terminating a session between the client and theserver associated with the first request; providing the client anotification page having a unique identifier, wherein the notificationpage includes an option to accept the response and an option to declinethe response and wherein the unique identifier is associated with theoption to accept the response; receiving at the processor of thefirewall appliance a second request for the content from the client,wherein the second request includes the unique identifier; and in theevent that the unique identifier remains valid, forwarding the cachedresponse to the client; wherein the content is only provided to theclient in response to the second request for the content from the clientgenerated in response to a selection of the option to accept theresponse in the notification page provided to the client.
 2. The methodrecited in claim 1, wherein the response comprises an executable file.3. The method recited in claim 1, wherein determining that the responseis not known to be safe comprises determining that the server is notincluded in a whitelist of trusted sites.
 4. The method recited in claim1, wherein the notification page has an associated timer that expireswithin a prescribed timeframe.
 5. The method recited in claim 1, whereinthe unique identifier remains valid if a time-out period for thenotification page has not expired.
 6. The method recited in claim 1, inthe event the unique identifier no longer remains valid, providing tothe client a second notification page in response to the second requestwith options to accept and decline the response, wherein the secondnotification page is associated with a different unique identifier. 7.The method recited in claim 1, wherein the content is not forwarded tothe client in the event that the option in the notification page toaccept the server response is not selected by a user of the client or inthe event that the option in the notification page to decline the serverresponse is selected by the user of the client. between the client andthe server for the same requested content.
 8. A system, comprising: aprocessor of a firewall appliance configured to: receive a response froma server to a first request for content originating from a client of aprivate network, wherein the firewall appliance is configured tointercept communications between the client and the server; determinethat the response is not known to be safe; cache the response to thefirst request at the firewall appliance; terminate a session between theclient and the server associated with the first request; provide theclient a notification page having a unique identifier, wherein thenotification page includes an option to accept the response and anoption to decline the response and wherein the unique identifier isassociated with the option to accept the response; receive a secondrequest for the content from the client, wherein the second requestincludes the unique identifier; and in the event that the uniqueidentifier remains valid, forward the cached response to the client; anda memory coupled to the processor and configured to provide theprocessor with instructions; wherein the content is only provided to theclient in response to the second request for the content from the clientgenerated in response to a selection of the option to accept theresponse in the notification page provided to the client.
 9. The systemrecited in claim 8, wherein the unique identifier remains valid if atime-out period for the notification page has not expired.
 10. Thesystem recited in claim 8, wherein the response comprises an executablefile.
 11. The system recited in claim 8, wherein to determine that theresponse is not known to be safe comprises determining that the serveris not included in a whitelist of trusted sites.
 12. The system recitedin claim 8, wherein the notification page has an associated timer thatexpires within a prescribed timeframe.
 13. The system recited in claim8, in the event the unique identifier no longer remains valid, theprocessor is further configured to provide to the client a secondnotification page in response to the second request with options toaccept and decline the response, wherein the second notification page isassociated with a different unique identifier.
 14. The system recited inclaim 8, wherein the content is not forwarded to the client in the eventthat the option in the notification page to accept the server responseis not selected by a user of the client or in the event that the optionin the notification page to decline the server response is selected bythe user of the client.
 15. A computer program product embodied in anon-transitory computer readable storage medium and comprising computerinstructions for: receiving at a firewall appliance a response from aserver to a first request for content originating from a client of aprivate network, wherein the firewall appliance is configured tointercept communications between the client and the server; determiningthat the response is not known to be safe; caching the response to thefirst request at the firewall appliance; terminating a session betweenthe client and the server associated with the first request; providingthe client a notification page having a unique identifier, wherein thenotification page includes an option to accept the response and anoption to decline the response and wherein the unique identifier isassociated with the option to accept the response; receiving at thefirewall appliance a second request for the content from the client,wherein the second request includes the unique identifier; and in theevent that the unique identifier remains valid, forwarding the cachedresponse to the client; wherein the content is only provided to theclient in response to the second request for the content from the clientgenerated in response to a selection &the option to accept the responsein the notification page provided to the client.
 16. The computerprogram product recited in claim 15, wherein the unique identifierremains valid if a time-out period for the notification page has notexpired.
 17. The computer program product recited in claim 15, whereinthe response comprises an executable file.
 18. The computer programproduct recited in claim 15, wherein determining that the response isnot known to be safe comprises determining that the server is notincluded in a whitelist of trusted sites.
 19. The computer programproduct recited in claim 15, wherein the notification page has anassociated timer that expires within a prescribed timeframe.
 20. Thecomputer program product recited in claim 15, in the event the uniqueidentifier no longer remains valid, further comprising computerinstructions for providing to the client a second notification page inresponse to the second request with options to accept and decline theresponse, wherein the second notification page is associated with adifferent unique identifier.
 21. The computer program product recited inclaim 15, wherein the content is not forwarded to the client in theevent that the option in the notification page to accept the serverresponse is not selected by a user of the client or in the event thatthe option in the notification page to decline the server response isselected by the user of the client.